Re: Looperlative LP1 - sample rate

[Ronan Chris Murphy <looper@venetowest.com>]

> Ronan-
> There are other much more complex sounding differences between square 
> and sine wave.  Boot up any analog synth and see for yourself.  
> Basically a square wave at any frequency contains all frequencies at 
> varying levels. Doesn't make much sense, but its true.  A sin wave 
> contains exactly one and only one frequency. jon.

A square wave is a wave that contains two states (one of which may or 
may not be zero) the effect of the "squaring or squareness"  of these 
waves is the inclusion of a series of harmonics including the octave 
and all odd order harmonics above the octave into a theoretical 
infinity. The first harmonic being the octave (or for instance 30k 
above a 15k square wave)

Something that contains all frequencies is called "noise". White noise 
contains all those frequencies evenly.


> Again, it's not so much about getting frequencies above 20K into our 
> loopers, rather it's
> about increasing the quality of sounds well within our hearing.  If 
> the frequencies at 20K are
> only allotted 2 samples per wave cycle, then an octave down only gets 
> 4 samples, 2 octaves down
> only gets 8 samples, and 3 octaves down which is right around 2.5K 
> only gets 16 samples per wave.
> Sampling at 192 would offer us 64 samples at 2.5K.  I don't know if my 
> math is correct, but this
> is how the numbers seem to be crunching.  Also, if my crunching is 
> correct, I'm not sure how
> perceivable this higher sampling rate actually is.  Perhaps someone on 
> this list has experience
> with these things?
>  Stephen

I think you are misunderstanding PCM sampling. At CD quality (44.1)  
there are 44,100 "snapshots" being taken of a sound per second. The 
same snapshot is used to capture all frequencies. It is not a matter of 
various samples being allotted to various frequencies. Therefor a 
waveform of 2.5k is captured 44.100 times per second. A frequency of 
25k could not be captured with 44.100 snapshots a second because that 
frequency would go between its positive and negative state 25,000 times 
a second, or 50,000 states a second. You could not capture that with 
44.100 snapshots a second.

If you are looking to improve quality of more commonly used frequencies 
you should be discussing bit depth which deals with the resolution of 
each of those snapshots. A commercial CD is 16 bit, most new pro audio 
gear is 24 bit. More importantly though for audio quality you should be 
looking at the quality of the Analog to Digital Converters, and the 
Digital to Analog Converts and the quality of the digital clock that 
those converters are referenced to. I would gladly take a high quality 
digital I/O and clock at 16 bit and 44.1 sample rate, over a low 
quality I/O and clock at 24 bit with a 96k sample rate. That would be a 
cool thing about making a looper with digital I/O you could hook up a 
nice Apogee digital I/O and clock to it.